The present invention relates to a device for tightening a rope, preferably an electric wire, for example an extension cord for electric apparatus or lamps, which is to be tightened along a wall or similar. More specifically the invention relates to that type of tightening device, which comprises a base member adapted to be attached to a support, a holding member adapted for the wire to be attached thereto and resilient means which in mounted condition of the devices exert a certain force between said members and thereby a tightening force on the wire.